Method and means for tuning electric oscillatory circuits



Dec. 5, 1939. G. GUANELLA METHOD AND MEANS FOR TUNING ELECTRIC OSCILLATORY CIRCUITS Filed April 14, 19:58'

INVENTOR.

ATTORNEY.

2,5` tion of an iron core inductance coil forming part tion of these devices has not as yet been found. @5;

hamaca. 5, 1939 2,132,377

UNITED STATES PATENT. OFFICE METHOD AND MEANS FOB TUNING ELEC- TRIC OSCILLATORY CIRCUITS Gustav Guanella, Zurich, Switzerland, assig-nor to Radio Patents Corporation, a corporation of New York Application April 14, 1938, Serial N0. 201,945 In Switzerland May 1, 1937 11 Claims. (Cl. Z50-40) The present invention relates to a method and a manner that the capacity of the condenser may means for controlling the tuning or natural frebe varied within the desired limits by a direct quency of an oscillatory or resonant electric cirbiasing potential impressed upon the electrodes. cuit or network and among the objects of the In its general construction this type of coninvention is to effect a tuning control directly by denser hereinafter referred to as blocking layer 5 and in accordance with an electric potential or or boundary layer condenser comprises a mecurrent without requiring any mechanically movtallic base. forming one electrode upon which is ing elements. applied a thin layer of a substance of W con- The problem oftentimes arises in practice of ductivity such as a layer of the oxide of the base 10 controlling the tuning or natural frequency of an metal similar to the construction of the known 10 oscillatory circuit or resonant network such as in dry rectifiers, or a layer of selenium or an equivathe case of remote control of a radio or like relent substance, said layer being ilrmly'united or ceiver Vor in automatic frequency or tuning ar` bonded to the base electrode and being in conrangements known as A. F. C. systems serving to tact with a second electrode either in the form adjust the tuning of a resonant circuit to the of a metallic layer sprayed or otherwise applied l5 frequency of a received radio signal in a receiver thereon or a separate electrode pressed into iirm or to a fixed standard frequency of a control deengagement with the blocking layer. Alternavice such as a piezo electric crystal in a high tively the second electrode may be in the form frequency oscillator or transmitter.' of a conducting liquid (electrolyte) serving to Arrangements have already been proposed for conduct the electric current to and from the 53o affecting the tuninginaccordance with a control blocking layer. Devices of this type block the potential without the employment of mechanielectric current-now in one direction and accordcally moving devices. Thus a tuning variation ingly act as a condenser in the blocking direction. can be eiected by controlling the 'premagnetiza- A complete satisfactory explanation of the funcof an oscillatory or resonant circuit. t'has also According to one theory accounting for various been proposed to provide an electronic valve serveffects and results, the blocking layer acts as a ing as a variable reactance element which may be dielectric similar as in a. condenser of ordinary controlled by adjusting a suitable biasing potenconstruction, however other phenomena including tial. The tuning of a resonant or oscillatory cirthe capacity variations caused by an impressed cult may be further effected by means of voltage biasing potential as utilized by the present invencontrolled impedances suitably connected to the tion can be better accounted for by the so-called circuit together with xed auxiliary capacity or gas film or boundary layer theory according to inductance elements. which a gaseous or boundary layer of molecular All of the known processes are subject to varidimensions exists between the base metal and the w ous disadvantages. On the one hand, the tuning blocking layer through which electrons can pass variations require considerable controlling eneronly in the direction to the metal electrode simigies and a substantial amount of additional aplar as in a vacuum valve. Whatever the function paratus resulting in increased cost while the tunand theoretical operation underlying such devices, ing variations obtainable areinmost cases insuiextensive experiments conducted by applicant J3@ cient for practical requirementsa have shown that substantial capacity variations By the present invention the drawbacks and in the current blocking direction may be effected disadvantages 0f the PIGVOUS methods are Sllbby and in proportion to anapplied direct biasing stantially overcome and substantial tuning variapotential, which capacity variations are utilized tions Obtained by small controlling energies and according to the present invention to control the with 8 minimum 0f auxiliary apparatus and Parts natural frequency or tuning characteristics of an required. oscillatory circuit or resonant network.

To this end, the invention contemplates the The invention will become more apparent from emDlOi/merlt 0f One 0r more COndEnSeIS having the following detailed description taken with refmechanically fixed electrodes. the electrical caerence to the accompanying drawing forming part m pacitance of which can be controlled by biasing of this specification and wherein; potentials impressed upon the electrodes. Such Figure 1 shows a diagram of a basic circuit for potential controlled condensers employed by the producing capacity variations according to the invention comprise a thin blocking or boundary invention,

u layer disposed between suitable electrodes in such Figure 2 shows an example for varying the tun- 55 ing or natural frequency of an oscillatory circuit, Figures 3uand 4 are modications of a circuit of the type according to Figure 2, l

Figure 5 shows a combination of the circuits ac- 5 cording to both Figures 2 and 3,

Figures 6 and 7 illustrate further modiiications of the invention, and

Figure 8 shows an exemplication of a potential controlled capacity element suitable for use in 10 connection with the invention.

` Similar reference numerals identify similar parts throughout thediiferent views of the draw- R'feierring to Figure 1, there is shown schematically by numeral I0, a boundary layer condenser of the general character described herein above which may be a selenium, copper oxide or any other suitable condenser andV of either the dry or liquid type. condenser in the example illustrated is connected in series with a iixed condenser Il Iof standard type. The terminals a-b of the series combination of both condensers I0 and Il may be connected in anycircuit such as an oscillatory or resonant circuit wherein the capacity variations are desired. 'I'he potential lcontrolled condenser III is-.biased in the blocking direction by a variable direct current potential suppliedfrom a suitable source such as a. battery I] in the example illustrated in connection with v a potentiometer I3 having a Variable tap for impressing a variable potential e upon the condnser III.

The biasing. potential controlling the capacity of the condenser III should be applied in such -a manner that the ldamping imposed bythe direct current uponthe oscillatory or tuned circuit in which the condenser I0 is connected remains within suiciently low limits and that no short circuit is formed for the biasing potential through the oscillatory circuit or associate network. For this purpose'the biasing potential e according to Figure 1 is applied from the po tentiometer I3 througha choke coil which offers a suiiiciently high impedance for the alternating currents in the associate circuits or network;`

This choke coil' may be replaced by a high ohmic resistance as shown in the subsequent illustrations. The biasing potential applied in this manner to the potential controlled condenser -I is blocked from the remaining portions of the associate network or circuit by the comparativelyA` Experiments have shown that the capacity of the potential controlled condenser depends to a large extent upon the frequency ot the currents or Vpotentials in the circuit in which thecondenser 05 is connected. This fact has to be considered in the design oi the oscillatory circuits or network. It the tuning of the'oscillatgry circuit is varied by a variable condenser auch as a rotary-contential controlled condenser (tine tuning adjust7 ment) xmay be taken into account by the proper design of the shape .of the plates of the rotary i. condenser in auch a manneras to maintain subdenser within widenmits .trough adjustment) -the diierent variations effected by the poareas?? stantially the same range of capacity variation for f all positions of the rough .tuning condenser.

Iteferring to Figure 2, there is shown an arrangement according to Figure l embodied in .an oscillatory circuit. In the example shown the potential controlled condenser circuit is connected in parallel to a resonant circuit comprising an inductance coil I5 shunted by a variable condenser I6. This circuit having vterminals c-d may be connected in an electrical system such' as a radio receiver whereby the tuning oi the circuit may be Varied within predetermined f limits by controlling the biasing potential supplied from the potentiometer I3. There is further shown in Figure 2 a high ohmic resistance I8 in place of a choke coil as shown in Figure 1 to block the alternatingpotentials in the associate circuit from the biasing potential circuit. Rough tuning is eiected by varying either the inductance of the coil I5 or the capacitance of the condenser I6. Invthe latter case as shown in the illustra.-

tion (variable condenser I6), the tuning variations for a predetermined change of the bias- 'y r tential controlled capacity I0 may be connected in series with the variable tuning condenser I6 such vas shown in Figure 3 in which case the blocking condenser II may be-dispensed with.

In this embodiment the tuning variations corresponding to a predetermined change of the biasvalue or amplitudeif undesired non-linear dis" tortion and reaction from the control circuitdue toI a rectifying action of the condenser or other causes-are to be avoided.

In circuits with great oscillating amplitudes it is advisable for this reason to provide several potential controlled condensers in series in place of a sing/le condenser as shown in Figure 2. /In thismanner the alternating voltage at each ot these condensers is prevented from exceeding a predetermined maximum limit. Under circumstances it is not necessary that all the capacities are voltage controlled and only a single voltage denser elements. l

A further possibility to prevent excessive alternating potential at the potential controlled condenser consists in connecting the same across a portion of the winding of the tuning inductance such as shown in Figure 5. According to the latter the condenser I0 is placed across the lower terminal of the inductance I5 and an intermediate tap point thereof suitably chosen to prevent excess alternating current loads on the condenser.

There are further shown in Figures 4, 6 and 7 exempliiications adapted to obtain substantially equal tuning variations for both low and high irequencies. In the example shown two potential controlled condensers I0 and I9 are provided, the average capacity of the condenser III being large comparedwith the average capacity of the condenser I9. Thus for high frequencies; that is, for

low values o1 the rough tuning condenser Ii, the

tuning is substantially effected .by variations o! the condenserl. It, on vthe other hand, the

capacity of the rough adiustingcondenser Il approaches the capacityfof the condenser Il for the low frequencies the tuning will be substantially anected by the capacity variations of the condenser Il. In this manner by the proper choice and design of the condensers In and Il it is possible to maintain a constant range of tuning variations for both high and low frequenciespi. e. within substantially the entire adiusting range of the rough tuning condenser. In Figure 4 which is equivalent to a combination of Figures 2 and 3 the potential controlled condenser Il is connected in parallel to the rough tuning condenser Il while the condenser Il is arranged in series with both the former condensers.

In the arrangement according to Figure 6 wherein one of the potential controlled condensers I0 is in series with the rough tuning condenser Il and the other potential controlled condenser Il is in parallel to both the former, both potential controlled condensers are arranged in series with the biasing potential source. In order to obtain the proper potentials across each condenser, either or both may be shunted by a high ohmic resistance of suitable value such as a ristance 20 connected across the condenser I0 in the example illustrated.

Figure 7 is substantially similar to Figure 4 with the exception that the condenser I8 is arranged in series with the inductance I5, the function and operation being otherwise similar to the preceding arrangements.

From the above it is seen that by suitable combination and circuit arrangement it is possible to obtain substantially equal tuning variations for different settings of a rough adjusting tuning element such as a variable condenser arranged in an oscillatory circuit or resonant electric network. This makes arrangements of this type especially suited for use in connection with automatic frequency control (A. F. C.) systems provided in radio receivers for automatically adjustingthe receiver to the frequency of a received radio signal. 'y Y The circuits shown are by'wayofexample only and it is understood that many modications and variations maybe resorted 'to' Acoming within the broader scope and spirit of the invention.

The biasing potential for varying the tuning of a resonant or oscillatory circuit according to the invention may be adjusted manually by the aid of a potentiometer as shown in the exempliiications illustrated. In the case of automatic tuning, this biasing potential is supplied by a discriminator arrangement generating a tune responsive or A. F. C. potential in accordance with any of the known methods. According to the latter as used at present in radio broadcast receivers, a direct potential is generated by the discriminator arrangement varying both as to sense and magnitude in accordance with the sense and amountof detuning of the receiver relative to a received signal frequency. If such an A. F. C. potential is applied to a potential controlled condenser suitably connected to an auxiliary circuit such as the local oscillator or tank circuit in a superheterodyne receiver, it is possible in this manner to effect an automatic tuning or frequency control of the receiver after the latter has been roughly brought into tune with the received signal frequency by means of a mechanical dial or the like. Alternatively, the arrangement according to the invention may serve for controlling or maintaining constant the frequency of an oscillaaisa's'n tor or transmitter by providing a frequency standard such as a piezo electric oscillator and' controlling the tuning of an oscillatory circuit of the main oscillator by a control potential varying in accordance with the deviations of both phase andfrequency of the oscillatory currents relative to the oscillations of standard frequency.M In general the invention may be utilized in con- Y nection with any system wherein the frequency of an alternating or oscillating current is to be balanced or synchronized with a second frelquency. Among otherv examples this is the case in common frequency broadcasting wherein the carrier waves transmitted from two or more stations have to be controlled and maintained in exact synchronism. f

In the use of a potential controlled condenser y according to the invention in a circuit or network provision should be made, as pointed out above, that the alternating load imposed upon the condenser does not4 exceed a permissible limit determined by the circuit and the behavior and characteristics of the condenser. For this purpose, it is desirable in most cases to provide the potential controlled tuning condenser in a special`pre= Stent value ,by 'special arrangements. This may be accomplished by the use of a known arrangef ment-for automatic volume control or by vvthe aid-54,()A

of amplitude limiting devices such as by tempera- 1 ture controlled resistances, regulating pentodes or hexodes which latter arel automatically regulated to maintain a constant amplitude of the oscillating current (automatic volume control).

Referring to Figure 8, there is shown a con-,

struction of a potential controlled condenser suited for use in connection with the invention. There is shown at 22 a metal plate or disc having applied thereon a thin blocking layer 23 of any suitable material described hereinabove. Item 24 is a second electrode of resilient metal having its outer portion pressed into firm contacting engagement with the layer 23 and being insulated from the disc 22 by an insulating washer orspacer 29. Further contacting electrodes 26 and 2l having extensions or connecting lugs 26' and 21', respectively, are placed in engagement with the electrodes 22 and 23, respectively, and the entire assembly bolted together by means of a metal screw 3l having a pair of locking nuts 32 and with a pair of further insulating washers 28 and 30 interposed between the screw 3i and the contact discs 26 and 21, respectively. It is understood the construction shown is by way of example only, various modications being possible as is obvious from the above.

Experiments have shown that with condensers of the above described type and other constructions similar to the known dry rectiers, electrolytic rectiflers or electrolytic condensers, substantial capacity variations may be obtained by varying biasing potentials. The electrical losses of the condenser may be kept within admissible limits by suitable design determined by experiments.

It has been found that in most cases the voltage controlled capacity variations are dependent 5 on a blocking layer having an extremely low electrical conductivity and a thickness of less than '-3 cm. According to experiments made, this blocking layer may be bounded by metallic or electrolytic conductors or semi-conductors 10 which latter exert an inuence on the capacity variations caused by the applied biasing or control potential.

By suitable choice of the semi-conducting layer it is possible to form therefrom the blocking layer of extremely low electrical conductivity. 'I'his can be obtained for instance by oxygen removal in the case of so-called oxidized semi-conductors (such as cuprous oxide, circonium dioxide, etc.) or by the addition of oxygen such as in the case of so-called reduced semi-conductors (such as zinc oxide).

The formation of the blocking layer from an adjoining semi-conducting layer is well known in the manufacture of blocking layer rectiers.

However, other processes have been proposed for the formation of the blocking layer and used successfully in the manufacture of blocking layer rectiers. Experiments have shown that the blocking layer can also be formed by special in- 80 sulating layers of suiiciently low thickness and which are bounded in a suitable manner by lay ers of conducting or semi-conducting material.

Such artificial blocking layers may for instance consist of organic lacquers such as shellac, Bake- $5 lite, nitro-cellulose lacquer and others.

A special type of potential controlled condenser are devices known as electrolytic rectifiers or dry and Wet electrolytic condensers wherein the blocking layer is produced by electrolytic forma- 0 tion. The variations of capacity depend to a large extent on the construction of the devices. Specially large capacity variations are obtained for instance with a tungsten anode placed in a copper nitrate electrolyte solution. Also by the 4,5 employment of niobium and tantalum as anode material substantial capacity variations by biasing potential control can be effected. The time constant of the capacity variation depends on the thickness and composition of the blocking 50 layer and adjoining electrodes and is of the order of several thousandths of a second. Apart from this rapid capacity variation a relatively slow action of the biasing potential is observed which is known as electrolytic formation depend- 55 ing on the forming Voltage.

Although devices of the above type known as electrolytic rectiers and electrolytic condensers may be used in certain cases without change as potential controlled condensers for the purposes 60 of the invention, it is preferable in many cases to vary the constants and composition of such devices such as the character of fixed electrodes, the composition of the electrolyte, the forming process, etc., to differ from the usual standards 65 and to conform with the new requirements and purpose. In many cases the direct current irnpedance should be as high as possible for the desired operating potentials to maintain the direct current losses at a 10W value. In general the l 70 direct biasing potential is applied in the blocking direction but in many cases it may be advantageous to apply a small bias in the current passing direction. Furthermore, it is possible to use devices of the above character wherein a blocking 15 action takes place in both directions. The blocking layer and if required the adjoining conductor or semi-conductor should be chosen and constructed in such a manner that the alternating Y current losses of such a condenser for the operating frequency within the biasing potential 6 range do not exceed the limits determined by the purpose and use of the condenser and that thev capacity variation is large compared with the loss resistance for the desired range of operating frequencies and biasing potential. 10

It will be evident from the above that the invention is not limited to the specic methods and arrangement of parts disclosed and shown herein for illustration but that the novel concept and underlying principle" of the invention is suscepl5 tible of numerous variations and modifications coming within the broader scope and spirit of the invention as defined in the appended claims. 'I'he specification and drawing are accordingly to be regarded in an, illustrative rather than in a 20' limiting sense.

I claim:

.1. The combination with a tunable circuit, of a polarized variable condenser arranged to form an eiective tuning element of said circuit, said 25 condenser comprising a pair of electrodes and a thin intermediate layer of low conducting material arrangedbetween said electrodes and being intimately united with at least one of said electrodes, a source of variable uni-directional potential, and means for impressing said potential upon said electrodes in the current blocking direction of said condenser.

2. The combination with an oscillatory circuit, of a polarized Variable condenser arranged to form an effective tuning element of said circuit, said condenser comprising a pair of electrodes and a thin intermediate layer of low conducting material arranged between said electrodes and being intimately united with at least one of said electrodes, a source of variable uni-directional potential, means for applying said potential to said electrodes in the current blocking direction of said condenser, and further means for blocking oscillating currents in said circuit from said source of uni-directional potential.

3. The combination with a tunable circuit, of a polarized Variable condenser arranged to form an effective tuning element of said circuit, said condenser comprising a pair of electrodes and a thin intermediate layer of low conducting material in contacting relation to said electrodes and having at least one surface thereof in intimate molecular contact with the adjacent electrode, a source of variable uni-directional potential, means for impressing said variable potential upon said electrodes in the current blocking direction of the condenser, and further means for preventing a short circuit of said source through said circuit.

4. The combination with a tunable electric circuit, of a pair of polarized variable condensers connected in series and parallel relation, respectively, to a tune determining element of said circuit, each of said condensers comprising a pair of electrodes and a thin intermediate layer of low conducting material in contacting relation to said electrodes, at least one surface of said intermediate layer being in intimate molecular contact with the adjacent electrode, a source of variable uni-directional potential, and means for impressing said variable potential upon said electrodes in the current blocking direction of said condensers.

5. The combination with a tunable electric cir- Vconducting material intimately and molecularly cuit comprising a rough tuning element, of a pair of polarized variable iine tuning condensers connected in series and in parallel, respectively, to a tune determining element of said circuit, each of said condensers comprising a pair of electrodes and a thin layer of low conducting material in contacting relation to said electrodes, at least one surface of said intermediate layer being in intimate molecular contact with the adjacent electrode, the average capacity of one of said condensers being large compared with the average capacity of the other condenser, a source of variable uni-directional potential, and means for impressing said unidirectionalpotential upon said electrodes in the current blocking direction of said condensers.

6. The combination with a tunable electric circuit comprising an inductance shunted by a variable condenser for rough tuning of said circuit, of a pair of polarized ilne tuning condensers, one of said polarized condensers being connected in parallel and the other polarized condenser being connected in series with said rough tuning condenser and having an average capacity which is large compared with the average capacity of said first polarized condenser, each of said polarized condensers comprising a pair of electrodes and a thin layer of low conducting material in contacting relation to said electrodes, at least one surface of said intermediate layer being in intimate molecular contact with the adjacent electrode, a source of variable uni-directional potential, and means for impressing said variable potential upon said polarized condensers in the current blocking direction.

7. The combination with an oscillatory electric circuit, oi a polarized variable condenser comprising a first electrode, a thin layer of low united to said electrode, a cooperating electrode in contacting relation to said layer, said condenser being connected in said tunable circuit to form an effective tuning element of said circuit, a source of variable uni-directional potential, and means for impressing said Variable potential upon said electrodes in the current blocking direction of said condenser.

8. The combination with an oscillatory electric circuit, of a polarized variable condenser comprising a iirst electrode, a thin layer of low conducting material molecularly united to said electrode, a cooperating armature in contacting relation to said layer, said condenser being connected in said circuit to form an eiective tuning element thereof, a source of variable uni-directional po-v tential, means for impressing said unidirectional potential upon said condenser in the current blocking direction, and further means for maintaining the oscillating potential developed across said condenser element below a predetermined limit.

9. In an arrangement as claimed in claim 8 with reference to said last means wherein said condenser is arranged so as to be subjected to a fractional portion of the alternating voltage developed in said circuit.

10. In an arrangement as claimed in claim 8 with reference to said last means wherein said condenser is connected in parallel to a portion of a time determining impedance of said circuit.

11. In an arrangement as claimed in claim 8 with reference to said last means, wherein said condenser being connected across a portion of a tuning inductance of said circuit.

GUSTAV GUAN'ELLA. 

